A new trend in the field of automotive fuel tanks is to make the fuel tanks out of a weldable polymer material, such as polyethylene, which lends itself to efficient manufacturing processes such as blow-molding. The use of these fuel tanks is becoming widespread; however, the prior art has not yet disclosed a suitable structure for connecting fuel tank rollover and vent valves to such polymeric tanks. The materials which lend themselves to efficient manufacture of polymeric fuel tanks typically are not suitable for making quality vent valves; they are frequently too soft and are subject to long term creep problems. Moreover, the preferred method for attaching ports to polymeric fuel tanks has been to weld them, using well-known techniques such as hot plate welding. The temperatures involved in the welding process can damage valve bodies made largely or entirely out of the same material as the fuel tank. However, harder, higher-melting temperature materials such as nylon, which are suitable for use in valve bodies, are difficult if not impossible to weld to the materials used for the polymeric fuel tanks. For example, polyethylene and nylon simply do not weld very well due to their different melting temperatures and other properties.
To overcome this problem, it has been known in the prior art to use a "grommet carrier" of a material similar to or the same as that of the fuel tank. The grommet carrier is annular and welded about a pre-formed aperture in the fuel tank. The grommet carrier includes portions for engaging seal or grommet structure on a standard valve body so that the valve can be connected to the grommet carrier in a sealing fit after the carrier has been welded to the tank. A drawback with this structure is that it requires separate welding and assembly steps when mounting the valve to the fuel tank, and the connection and seal between the valve and the grommet carrier are not suitably secure. It is also more expensive to manufacture.
There is accordingly a need for a weldable vapor vent valve structure in which standard non-weldable vent valves can be efficiently and securely welded to a polymeric fuel tank.